LONG-LIVED TOPOGRAPHY ALONG RIFTED MARGINS: INSIGHTS FROM APARADOS DA SERRA ESCARPMENT, SOUTHEAST BRAZIL

Mauricio Barcelos Haag , Scott Jess, Lindsay M. Schoenbohm, Eva Enkelmann, Taís F. Pinto

The Brazilian margin is one of the longest elevated passive margins (EPMs) in the world. However, both the timing of uplift and the long-term evolution of this EPM remain highly debated. In this study, we present a new suite of apatite (U-Th-Sm)/He (AHe) and fission track (AFT) ages for the southern end of the Brazilian EPM, in the Aparados da Serra plateau. Our results reveal that mean AHe ages range from 43 – 112 Ma, while AFT ages range from 46 – 222 Ma. Thermal history models suggest monotonic exhumation rates in the Aparados da Serra, with post-rifting rates less than 50 m Myr-1 in the coastal plain and < 25 m Myr-1 in the volcanic plateau. Collectively, our results imply a total erosion of 2 – 4 km of material from the coast and less than 2 km from the plateau since rifting ca. 120 – 100 Ma. AHe and AFT data indicate no detectable exhumation during the Cenozoic, implying that recent uplift along the margin was either absent or minimal, and that the relief observed in the Aparados da Serra is a likely consequence of sustained rift topography. Based on the absence of major recent tectonic events, we argue that Cenozoic exhumation patterns in the Aparados da Serra were largely controlled by geomorphologic processes (e.g., differential erosion). The spatial distribution of AHe ages indicates that the Aparados da Serra evolved through escarpment retreat, at least across the region extending from the present-day coastline to the escarpment position. Lastly, the equivalence between long (AFT and AHe) and short-term (catchment-averaged) erosion rates argues for sustained stability of the margin over geological timescales.